1. Field of the Invention
The present invention relates to the technology of coating by high-temperature atomization, more particularly to an apparatus for coating by detonation waves. The invention may find application in metallurgy, chemistry, power and mechanical engineering, and other branches of industry where the requirements placed upon the products are such that these products be made entirely from the coating material either by casting or by caking.
2. Description of the Prior Art
The quality of coating produced by the method of detonation waves depends mainly upon the temperature and velocity of the coating material particles. Hence, in the preceding apparatus for coating by detonation waves, comprising originally a detonation chamber, a device for firing the explosion, a gaseous mixture delivering system and a powdered material feeding system (see U.S. Pat. No. 2,714,563), whose construction practically remained unchanged, the improvements aimed at perfecting the quality of coating have been made mainly in the systems for feeding gaseous mixture and the powdered material to the detonation chamber, the aforementioned parameters depending upon the functioning of said feeding systems.
Constructional changes in the gaseous mixture delivering system were aimed at the provision of homogeneity of the gaseous mixture delivered to the detonation chamber, which is required to maintain optimum thermodynamic parameters of the coating process.
Numerous improvements introduced in the powered material feeding system were aimed at the optimization of the place, time, and speed of injection of powdered material into the detonation chamber (see "Engineering of the Metal-Working Industry: Detonation Coatings and Their Uses", Niimash Publishers, Moscow, 1977, pp 25-30). However, one factor has not been taken into account, which factor substantially affects the quality of coating, namely, uniformity of the quantity of powdered coating material introduced in the detonation products. Besides, to stabilize the batch of powder being fed to the detonation chamber and interacting with the products of detonation is one of the primary conditions necessary for obtaining high quality coating. At the same time existing apparatuses for coating by detonation waves practically do not provide for a stable rate of feeding of powder into the detonation chamber, which is explained by the instability of the physical properties of the powder as well as by obstructions in the powder feeding conduits, conditioned by the coating technology.
Known in the art is an apparatus for coating by detonation waves, comprising a detonation chamber in the form of a barrel closed at one end, a spark plug mounted in the barrel, a powder feeding system, and a gaseous mixture delivering system, both communicating with the detonation chamber (see U.S. Pat. No. 3,884,415). The gaseous mixture delivering system comprises a mixer communicating with the sources of the gaseous mixture ingredients. The powder feeding system comprises a batchmeter having a hopper for powdered coating metal and a tubular body communicating with the detonation chamber through a delivery pipe. Connected with the tubular body is a gas conduit connecting the batchmeter with the source of a carrier gas. At the outlet of the gas conduit there is installed a valve. In the tubular body there is mounted a slide valve simultaneously serving as a splitter.
The apparatus also comprises a control system including a control unit having a driver unit electrically connected to the gaseous mixture delivering system, the spark plug and the powder feeding system through their respective control circuits.
The powder is fed to the detonation chamber when in response to a signal received from the control unit the batchmeter opens. Carrier gas enters the cavity of the tubular body and moves the slide valve so that the tough formed therein, preliminarily coinciding with the hopper outlet and filled now with the powder, coincides with the delivery pipe connecting the tubular body with the detonation chamber and the by-pass conduit communicating with the cavity of the tubular body filled with the carrier gas. As a result, a batch of powder in the trough of the slide valve is injected into the detonation chamber.
Despite constant volume of the trough in the slide valve, which determines the amount of powder fed to the detonation chamber, the detonation chamber volume may vary, because with the decrease of the powder level in the batchmeter bunker the rate of the powder flow also decreases, which in turn results in a decreased amount of powder entering the trough of the slide valve. In addition, the quantity of powder in the batch may decrease with the decrease of the clear opening of the delivery pipe due to choking or partial sculling thereof. Decreased amount of the powder being fed to the detonation chamber leads to overheating and burning of the powder during the explosion.
Besides, as the absolute value of mechanical losses of powder practically does not depend upon its amount in the detonation products, in case of small batches the part of the above losses relative to the initial quantity of the powdered coating material increases, thereby affecting economic efficiency of the coating technology.